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Soil is a favorable habitat for microorganisms inhabited by a wide range of microorganisms, including bacteria, fungi, algae, viruses and protozoa. Microorganisms are found in large numbers in soil - usually between one and ten million microorganisms are present per gram of Soil. Soil As A Natural Microbial Environment

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Almost every chemical transformation taking place in soil involves active contributions from soil microorganisms. Active role in soil fertility as a result of their involvement in the cycle of nutrients like carbon and nitrogen, which are required for plant growth. Responsible for the decomposition of the organic matter entering the soil and therefore in the recycling of nutrients in soil. Certain soil microorganisms such as mycorrhizal fungi can also increase the availability of mineral nutrients (e.g. phosphorus) to plants. Soil As A Natural Microbial Environment

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First Example Deposition of solid waste. The solid wastes like garbage destroy the natural beauty and become a breeding ground for mosquitoes which spread diseases like malaria and Dengue. Land Pollution caused by acid rain reduce the fertility of soil leading to reduction of crop yields.

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Second Example As a kind of indirect contamination: The use of treated wastewater for agricultural irrigation, percolation of contaminated surface water to subsurface strata, oil and fuel dumping or leaching of wastes from landfills. A range of bacterial pathogens, introduced through contaminated irrigation water or manure, are capable of surviving for long periods in soil and water where they have the potential to contaminate crops in the field.

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Third Example The use of excess fertilisers to increase the crop yields makes the soil either acidic or alkaline and pollutes it. For example, excessive use of ammonium sulphate fertilisers makes the soil highly acidic whereas the excessive use of sodium nitrate fertilisers makes the soil highly alkaline. This differences in pH affect the growth of essential and beneficial Microorganisms for healthy soil.

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The Most Common M.O. ESPECIALLY common microbe in SOIL – Actinomyces, (genus) this MICROBE produces an enzyme – geosmin, TOPSOIL this is the distinct smell given to TOPSOIL SOME strictly DONT utilise O 2 OTHERS can utilise O 2 OR chemicals tolerates dry conditions when other microbes cant

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HOW is the Soil Sample Prepared for Examination? Extraction of soil is done with a hollow rod to a depth of 10-15 cm Samples are filtered to remove: stones/ roots/ finer fibres: size 2mm Storage is at 4 o C SAMPLES are taken in squares at appropriate spacings to ensure all land variations are included; it is quite an extensive process

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Microbial Examination of Soil Procedure: 1.Under aseptic conditions, pour cooled (45˚C)nutrient agar in sterilized petri dishes as much as 15-20 mL for each. 2.Using a balance, add 1 gm of soil sample to a 9mL of sterilized dist. H 2 O tube. This will make the first dilution 1:10 3.Make a serial dilution, by transform 1 ml of 1:10 tube to another 9mL tube and repeat this until 1:10 6 4.Using a new pipette, Transfer 1 ml of each dilution into a nutrient agar plate, and spread the inoculum using sterilized glass spreader 5.Incubate the dishes on 22-25 ˚C for at a weak at least

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Microbial Examination of Soil 6- Count only the plates contain 30 -300 colonies. 7- Count each kind of microorganisms, like Bacteria 12 colonies, Fungi 3 colonies, Actinomycetes 6 colonies, etc. 8- Multiply the total number with the dilution factor and the unit is (CFU colony forming unit/1 gm of soil) 9- Record the results in the following table. 10- Write the inference and the conclusion of this experience.